1. Field of the Invention
The present invention relates, in general, to high power magnetrons and, more particularly, to a magnetron that is capable of reducing its thermal stress by varying the inside diameter and thickness of the cylinder of its anode, thereby improving the thermal stability of the anode.
2. Description of the Prior Art
As well known to those skilled in the art, magnetrons are devices for transmitting to the outside microwaves that are generated when an anodal current is applied. The magnetrons may be classified into magnetrons for electronic ranges and high power magnetrons. The magnetrons for electronic ranges or ovens can be employed to generate microwaves of a high frequency in electronic ranges, while the high power magnetrons can be employed in industrial purposes. Since the magnetrons generate a considerable amount of heat, the magnetrons generally are provided with cooling mechanisms. The magnetrons for electronic ranges are chiefly provided with air-cooling type cooling mechanisms, while the high power magnetrons are provided with either air or liquid-cooling type cooling mechanisms. The air-cooling type cooling mechanisms are employed for high power magnetrons generating relatively lower power, while the liquid-cooling type cooling mechanisms are employed for high power magnetrons generating relatively higher power.
As depicted in FIG. 1, a conventional high power magnetron employing an air-cooling type cooling mechanism includes a cylinder 11 positioned at its center portion. A plurality of vanes 12 and straps 13 are positioned in the cylinder 11, and form a resonance circuit when an anodal current is applied. A cathode 14 is positioned between the vanes 12, and serves to radiate a large number of thermions and to generate microwaves in an operation space between the cathode 14 and the inner ends of the vanes 12. An antenna 15 is mounted to transmit microwaves generated in the operation space. A plurality of cooling fins 16 are arranged around the cylinder 11, and serve to dissipate heat into which the remaining energy, which is not converted into microwaves, is converted. A pair of yokes 17 and 18 are respectively positioned over and under the cylinder 11, and serves to protect and support the anode and cooling fins 16 and to guide external air to the cooling fins 16. A pair of permanent magnets 19 are respectively positioned on the inner surfaces of the yokes 17 and 18, a filter box 20 is positioned on the outer surface of the lower yoke 18, and the permanent magnets 19 and the filter box 20 constitute a closed magnetic circuit.
As shown in FIG. 2, the anode of the magnetron comprises the cylinder 11, a plurality of vanes 12 mounted in the cylinder 11 and straps 13 mounted through the vanes 12 and forming a resonance circuit together with the vanes 12.
The high power magnetron constructed as described above generates microwaves of a high frequency and transmits these to a system.
When a predetermined amount of anodal current is applied to the cylinder 11, a resonance circuit is formed by the vanes 12 and the straps 13 in the interior of the cylinder 11 sealed under vacuum. If the resonance circuit is formed, microwaves are generated in the operation space between the inner ends of vanes 12 and the cathode 14. The generated microwaves are transmitted to the system through the antenna 15.
In such a case, most of energy generated in the operation space is converted to microwaves, but some of the energy remains and is converted to heat. This converted heat is conducted to the vanes 12 through the operation space and is dissipated outside of the cylinder 11. The heat dissipated through the cylinder 11 is cooled by means of a plurality of cooling fins 16 because the cooling fins 16 are arranged around the cylinder 11.
Briefly, in the conventional high power magnetron, when the cathode 14 is heated, most of energy is converted into microwaves, and the remaining portion of the energy converted to microwaves is converted into heat and transmitted to the vanes 12.
At this time, the vanes 12 are thermally deformed and extended radially, and the straps 13 mounted through the vanes 12 receive heat and are extended radially. Since the straps 13 are partially welded to the vanes 12, thermal stress corresponding to the difference between the thermal coefficients of the vanes 13 and the straps 13 causes the straps 13 and the vanes 12 to be deformed.
The portions of the straps 13 that are not welded to the vanes 12 may be severely deformed owing to the fixing force created on the welded portion of the straps 13.
In addition, the deformation of the vanes 12 is affected by the deformation of the cylinder itself 11 owing to heat transfer to the cylinder 11. For example, when the amount of the deformation of each vane 12 exceeds the amount of the deformation of the cylinder 11, contracting force is radially exerted on the vanes 12. On the other hand, when the amount of the deformation of each vane 12 is less than the amount of the deformation of the cylinder 11, the vanes 12 are radially elongated toward the cylinder 11.
The parts of the anode are under severe thermal stress because deformation occurs owing to their complicated mechanical connection and force is generated to resist the deformation.
The thermal stress is concentrated on the straps 13, and the straps 13 easily reach fatigue fracture. The life span of the magnetron generally depends upon the life spans of the cathode 14 and the straps 13. Accordingly, with regard to a magnetron, the sizes of its parts should be designed to be appropriate from a thermal point of view in connection with the power of the magnetron.
In a conventional high power magnetron of 1.7 KW, since its heat loss is great, the thickness of the cylinder of its anode is designed to be about 3.5-4.0 mm, on an average, 3.8 mm.
However, in such a case, since the deformation of the vanes 12 and the straps 13 and the deformation of the cylinder 11 are connected in a manner that is complicated, the thermal stability of the magnetron is deteriorated and the fabrication costs of the magnetron are increased owing to the excessive thickness of the cylinder 11.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a magnetron that is capable of not only reducing the thickness of its cylinder but also improving the thermal performance of the cylinder, thereby improving thermal stability of the cylinder, lengthening the life span of the cylinder and reducing the fabrication costs of the cylinder.
In order to accomplish the above object, the present invention provides a magnetron including an anode, the anode having a cylinder positioned around a cathode, a plurality of vanes radially fixed to the inner wall of the cylinder, and straps mounted through the vanes, wherein the inside diameter of the cylinder is 40-43 mm and the thickness of the cylinder is 2.8 mm or less.